Generally, an organic compound based electronic device represents an electronic device which can process or transform electronic, magnetic, or optical signals with organic molecules. Commercial examples of the organic compound based electronic device include a liquid crystal display device, an organic light emitting diode, and so on. In a narrow sense, the organic compound based electronic device also represents an electronic device having a molecular size, for example, a molecular memory, a molecular switch, a molecular rectifier, a molecular wire, and so on. Because most of molecules have the size of several nanometers, the organic compound based electronic device is called as “molecular nano-electronic device”.
The molecular electronic device has advantages in its size, function, mass production, and so on, compared with a conventional semiconductor device. Specifically, the size of a molecular electronic device is much smaller than that of a silicon device. Thus, it is possible to produce an electronic device of large scale integration with the molecules. In addition, a molecule may have various functions. For example, in a conventional silicon technology, both of transistors and capacities are necessary to produce a memory. However, in a molecular electronic device, a molecule can work as a memory. Also, by using the molecule's self-assembling properties, tens of millions or hundreds of millions of devices can be simultaneously assembled in a solution state, and accordingly the cost of equipment and facilities for manufacturing the electronic device can be innovatively decreased. Considering the cost for increasing the integration degree of a semiconductor, there should be a limitation in increasing the integration degree of a semiconductor. For example, it is known that Intel Corporation spent 12 thousand dollars in building a semiconductor manufacturing factory on 1968, but on 2000, spent almost 12 million dollars in building a factory having the same capacities. That is, the cost will increase by a geometric progression as the integration degree increases. In other words, because of costs of equipment and facilities rather than lacks of the integration technology, there is a limitation in increasing the integration degree of a semiconductor. After all, in 20 to 30 years from now, the Moore's Law may not work. To solve these problems, a study on a molecular electronic device is necessary.
Aviram and Ratner proposed a theoretical molecular diode in 1974, in which a molecule was interposed between two metal electrodes. Reed of Yale University, Tour of Rice University, and so on proposed a sandwich structure device showing a Negative Differential Resistance (NDR) effect, by locating nano-pore membrane having electron donor and electron acceptor functional groups between two metal electrodes. FIG. 1 is a structure of a conventional molecular electronic device showing Negative Differential Resistance (NDR) characteristics and a graph showing the current (nA)−voltage (V) characteristics thereof. As shown in FIG. 1, a molecule is interposed between a pair of electrodes by covalent bonding to form a molecular electronic device. The device works as a diode which transmits currents at a predetermined voltage. However, in the conventional molecular electronic device, a single molecular layer having the average size of less than 10 nm must be positioned between metal electrodes. Thus, there are disadvantages that the production cost is high and an electronic short between the electrodes may easily occur. The electronic short deteriorates the uniformity of the electronic device, and makes it difficult to commercially use the molecular electronic device.